An attempt to perform a graft polymerization of (meth)acrylic acid with respect to a polyether compound has been made in various fields, such as polyurethane, etc. For example, (1) Japanese Laid-Open Patent Application No. 71710/1980 (Tokukaisho 55-71710) discloses a polymer obtained by a graft-polymerization reaction of acrylic acid with a polyoxyalkylene compound wherein the acrylic acid is used in an amount of 3 to 15 percent by weight with respect to the total amount, and the manufacturing method thereof. However, when the graft polymer obtained by the described method of the Gazette (1) is used as a detergent builder, dispersant such as an inorganic pigment, etc., a fiber treatment agent, etc., the amount of carboxylic group, i.e., the amount of carboxylic acid is small, and the anti-gelation properties are poor, and a calcium ion capturing ability is too low. For the described disadvantageous characteristics, the graft polymer obtained from the described method does not offer sufficient performances, or requires a significantly increased amount of the graft polymer in order to ensure satisfactory performance.
Here, the anti-gelation properties are shown by numerical values indicative of easiness in mixing a graft polymer with a surface active agent. The lower the values, the more superior the anti-gelation properties. Namely, low anti-gelation properties suggest that the graft polymer can be mixed with the surface active agent with ease without generating clod. On the other hand, the calcium ion capturing ability shows detergency (washing power) of a detergent composition containing the graft polymer by a numerical value (mgCaCO.sub.3 /g) obtained by converting an amount of calcium ion that is captured by 1 g of graft polymer into calcium carbonate. The higher the value, the more desirable is the detergency.
In the described manufacturing method, when a graft polymerization of a hydrophilic ethylenically unsaturated monomer in an amount of not less than 25 percent by weight with respect to the total amount is performed, a large amount of carboxylic acid is generated, i.e., the concentration is too high. Thus, when adopting such graft polymer for the aforementioned purposes, the anti-gelation properties are too low.
(2) Japanese Laid-Open Patent Application No. 62614/1984 (Tokukaisho 59-62614) discloses a polymer obtained by performing a graft polymerization of not less than 20 percent by weight of hydrophilic ethylenically unsaturated monomer based on the graft polymer with polyglycol ether having at least one hydrophobic group, and the manufacturing method thereof. For the described manufacturing method of the Gazette (2), a method of adopting a solvent such as water, toluene, etc., and a method of carrying out a reaction at 90.degree. C. or below without using a solvent are known.
However, the method has a drawback of low grafting efficiency, and thus the resulting graft polymer contains many ungrafted polymers, thereby presenting the problem of poor anti-gelation properties. Therefore, when such graft polymer is used as the detergent builder, the dispersant such as the inorganic pigment, etc., sufficient performances cannot be obtained. On the other hand, when the graft polymer resulting from the described method is used as the detergent builder of the detergent composition in a liquid form, ungrafted polymer is separated.
(3) Japanese Laid-Open Patent Application No. 177406/1991 (Tokukaihei 3-177406) discloses the same graft polymer obtained by carrying out a graft polymerization in an aqueous solvent. However, the method of performing the graft polymerization in an aqueous solvent has a drawback of low grafting efficiency. Therefore, the polymers resulting from this method are mainly polycarboxylic acids which are not grafted, thereby presenting the problem of poor anti-gelation properties. Therefore, when the graft polymer resulting from the method of the Gazette (3) is used for the described purposes, desired performances cannot be obtained.
As described, the conventional techniques do not enable a graft polymer which shows a high grafting efficiency and contains small amounts of ungrafted polymer while showing a calcium ion capturing ability and a anti-gelation property in respective specially defined optimal ranges to be manufactured with ease. Namely, the conventional techniques do not enable a water-soluble polymer which shows significantly improved detergency and satisfactory performances, for example, as a detergent builder, to be manufactured with ease.
The present invention is achieved in the hope of finding a solution to the described problems associated with the conventional technique, and accordingly, an object of the present invention is to provide a water-soluble polymer having a calcium ion capturing ability in a specially defined optimal range and a anti-gelation property in a specially defined optimal range, that can be suitably used, for example, as a detergent builder by enabling a significantly improved detergency and satisfactory performances to be obtained, and also to provide a manufacturing method of such water-soluble polymer and a detergent composition containing the same.